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    SubjectRe: [patch 5/6] mm: simplify vmscan vs release refcounting


    On Thu, 19 Jan 2006, Nick Piggin wrote:
    >
    > The VM has an interesting race where a page refcount can drop to zero, but
    > it is still on the LRU lists for a short time. This was solved by testing
    > a 0->1 refcount transition when picking up pages from the LRU, and dropping
    > the refcount in that case.

    Heh. Now you keep the count offset, but you also end up removing all the
    comments about it (still) being -1 for free.

    And your changelog talks about "atomic_inc_not_zero()" even though the
    code actually does

    atomic_add_unless(&page->_count, 1, -1);

    which makes it pretty confusing ;)

    I also think it's wrong - you've changed put_page_testzero() to use
    "atomic_dec_and_test()", even though the count is based on -1.

    So this patch _only_ works together with the next one, and is invalid in
    many ways on its own. You should re-split the de-skew part correctly..

    Linus
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